Abstract:
Capillary electrophoresis with an indirect photometric detection was
developed for the analysis of non-chromophore alkylphosphonic acids (fosfomycin,
dihydrogen phosphate, ethylphosphonic acid, clodronate and alendronate). The
development of method was comprised of optimizing the concentration of benzoic
acid (15-30 mM) and pH of the background electrolyte (BGE) (4.0-7.0), the multiple
co-ions probe BGE (addition of salicylic acids), temperature (20-30 OC) and applied
voltage (-25 and -30 kV). Since the use of a single probe BGE did not give a
symmetrical peak for clodronate and alendronate due to differences in mobilities, the
multiple co-ions probe BGE was employed and optimized. The use of an additional
probe, salicylic acid, improved the alendronate peak shape, but clodronate was
slightly fronting. As a compromise, the optimum CZE condition was a BGE
containing 30 mM benzoic acid (pH 3.8), 5 mM salicylic acid and 0.5 mM
cetyltrimethylammonium bromide (CTAB). The temperature of 30 OC and the applied
voltage of -30 kV. The condition provided a baseline separation of all analytes in 5
min with the resolution of > 2.19, number of theoretical plate of > 35,291 and tailing
factor of 0.54-3.03. Method validation showed good linearity (r2 > 0.999) and
precision (%RSD < 2.67% for migration time and < 2.47% for peak area). Recoveries
were in a range of 97.4-103.6% for fosfomycin, clodronate and alendronate. The
limit of detections were 8, 8, 6, 30 and 50 μg/mL for fosfomycin, dihydrogen
phosphate, ethylphosphonic acid, clodronate and alendronate, respectively. The limit
of quantitations were 20, 20, 15, 100 and 80 μg/mL for fosfomycin, dihydrogen
phosphate, ethylphosphonic acid, clodronate and alendronate, respectively. Finally,
the validated method was successfully applied for the determination of fosfomycin,
clodronate and alendronate in pharmaceutical formulations available in Thailand